Grain to Whisky ratio question...

Interesting question. I guess it's best to mail some distilleries directly and ask them. I am sure they will try to help you. Hope you share the infos with us.

The spirit yield is expressed as litres of pure alcohol per tonne (a "full cask" is irrelevant here, can be 50 or 500 litres, and before it's "whisky" some of it will have evaporated). Mind that it's counted as pure alcohol and casks are filled at around 65-70%.

Malt producers usually set a typical minimum yield for one tonne of malted barley is around 405 liters. Nowadays every distillery is trying to improve this and most are around 420 liters.

The rest of the math is simple: 420 at 100% means 910 litres at 46% alcohol or +/- 1300 bottles of 70cl. Then you'll have to take into account the angel's share which depends on the cask type and the age, so the actual number of bottles you can fill will be significantly lower (1,5 - 2% will be lost a year). Roughly you could say that one kilo of barley produces one bottle of whisky.

@WhiskyNotes. - what a wonderful set of answers. Thank you!